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Computers are a necessary part of
life. Individuals look at computer screens from the moment they wake to the moment they go to sleep. Not only are computers being used for professional use, but recreational use has grown tremendously with the popularity of social sites such as Facebook and games like World of Warcraft. With this increase in computer use, eye fatigue is a common and expected side effect.
Why does eye fatigue occur?
Eye fatigue, or asthenopia, is a weakness of the eye that can cause pain, dimmed vision, double vision, nausea and several different types of headaches. The kind of asthenopia that is associated with computer use is accommodative asthenopia, which is due to a strain of the ciliary muscle. To understand what this means, the ECP must have a broad understanding of accommodation. Accommodation, in simple terms, is the change that the eye goes through to enable a person to see an object at various distances. Accommodation is a multistep process that involves the crystalline lens, ciliary muscles, a cranial nerve and the Zonules of Zinn. How the process works is the:
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Brain recognizes a blurred near or intermediate image
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Cranial nerve III (oculomotor) is activated. This nerve controls accommodation, papillary constriction and ocular convergence
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Eyes converge as the medial recti muscles contract and the pupils undergo miosis, or constriction
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Ciliary muscles contract and moves toward the crystalline lens, causing the crystalline lens to move forward
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Zonule fibers relax and cause the crystalline lens to bulge, increasing its power
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Light is refocused through the lens so that the image falls on the retina
Now, when an individual concentrates on something at a close or intermediate distance, the ciliary muscles are in a constant state of contraction. As the contraction continues fatigue sets in and the muscles are forced to begin to relax. When the muscles begin to loosen, the crystalline lens flattens and the image starts to blur slightly. This constant state of contraction can also lead to pain in and around the eye, squinting, headaches as well as a condition known as pseudomyopia.
Pseudomyopia is a spasm in the ciliary muscle caused by a constant state of ciliary contraction. When a spasm occurs, distance objects become blurry because the crystalline lens remains in a constant state of accommodation. The eye would then be in a myopic state due to the fact that the eye is now over plus in power from the spasm. All of the images would be focused before the retina just like in traditional myopia. When the spasm releases, vision would go back to normal.
In the case of the computer, this situation is aggravated by the construction of the image that the patient is trying to view. Computer images are created by pixels or small dots that are aligned to create the image. However, a pixel does not have the same sharp definition that the printed counterpart contains. This causes the eyes to work harder trying to see the computer image. In addition, the computer screen has a refresh rate that re-draws the screen every so often. This causes further strain on our accommodative mechanism as we try to follow this movement unconsciously. Finally, the glare from the screen and/or the overhead lighting can cause even further accommodative strain.
Correcting the Fatigue
One of the easiest ways to treat computer eye fatigue syndrome is to provide the patient with computer lenses. By providing spectacle lenses formulated just for computer distance, accommodation relaxes and eyestrain and blurred vision is reduced. The hard part is trying to convince a patient that he or she needs a separate pair of glasses for the computer.
Computer glasses are needed for the unusual distance most computers are set in relation to the eye. They are usually positioned 20 to 26 inches from the eye, closer than distance or driving visual needs and farther away than near or reading visual needs. Glasses are not commonly prescribed for this distance. Most single vision glasses are prescribed to correct near or far vision. Bifocal lenses correct near and far but neglect the intermediate area, and other multifocals such as progressives and trifocals have only a small area dedicated to this zone and are inadequate for long time computer use. This inadequacy stems from the unusual head position required to view most computer screens through a progressive or trifocal.
Choosing the Appropriate Lens
Intermediate Single Vision only Lens
This computer lens is designed to have only the prescription for computer distance throughout the whole lens. If the patient is in a multifocal prescription, the ECP must take half of the add power and add it to the distance. This provides the intermediate power correction for most cases. The benefits to this lens are that it provides the widest intermediate area possible with no image jump or possibly distracting lines. The main drawback is the lack of a near area. This can be a serious problem because many who work on a computer usually have to look at a near distance also if only to see the keyboard.
Flat Top Occupational Lens
A modified flat top is a very successful way to ease computer eye fatigue syndrome. The portion of the lens that is usually prescribed to treat distance is modified for intermediate use and the segment remains for near use. To do this, the ECP must create a new add power that is usually 50% of the original add power. This is important because otherwise the near power will be too strong and the lens will be unusable.
Although all bifocal widths can be used, the flat top 35 (or wider) is usually the most effective choice. The benefits to using a flat top 35 are very wide, useable areas, the least amount of distortion, and two powers in one lens. The drawback is a line that some patients will find unflattering or distracting. It is important to stress that these spectacles are strictly for the computer/office work and should be left at the work station.
Customized Occupational Progressives
With baby boomers increasing both their occupational and recreational computer use at a significant rate, many lens companies have developed a progressive lens for computer use. Usually designed to correct for distances of 12 to 48 inches, these lenses offer numerous benefits to the fashion forward individual. The distracting line is removed, image jump is eliminated, and the patient may already be accustomed to progressives in their dress wear. Some of the best occupational progressives on the market today are the Shamir Office; Zeiss Gradal RD and Zeiss Business; Sola Access; and Essilor Computer.
The Shamir Office uses a system that the company calls Dynamic Power. Dynamic Power is a slow reduction of power as the lens moves from intermediate to near and is classified by the amount of power that is subtracted from the near power to reach the intermediate distance. Dynamic Power is available in four design classifications: -0.75, -1.25, -1.75, -2.25. This system is achieved through a proprietary free form manufacturing techniques termed Eyepoint Technology that creates a wide, edge to edge, clear visual path from the intermediate to near areas.
The Carl Zeiss Company manufactures the Zeiss Gradal RD, Zeiss Business and the SOLA Access. Each lens is designed to meet the different needs of a patient based on his or her professional and recreational habits. The Zeiss Gradal RD is designed for distances of 10 feet or closer, called Room Distance (RD) by the company. It provides clear vision for all indoor activities and eliminates the “head bobbing” that commonly occurs with traditional progressives.
The Zeiss Business lens is a short corridor lens that can fit in the smaller frames and is developed for distances up to 4 feet. The Sola Access is developed to give high quality vision at distances up to 7 feet while providing an exceptionally wide near area and a larger intermediate area than traditional progressives. The intermediate area width varies based on the strength of the prescription.
Essilor has developed a lens called the Anti Fatigue Lens. It is different than traditional computer lenses because it is intended for full time wear and it does not follow a progressive type lens design. It has a power boost at the bottom of the lens of a little over a half a diopter that helps to ease eyestrain and fatigue. The lens is intended for myopes experiencing fatigue and emerging presbyopes, making it an excellent lens for those with computer eye fatigue once it has been prescribed.
When ordering occupational progressives, be sure to follow the manufacturer’s guidelines.
Base-In and Base out Prism Lenses
Horizontal prism lenses may be prescribed when the eyes are not converging appropriately. When the eyes do not converge adequately, a binocular dysfunction occurs resulting in eyestrain and blurred vision. Convergence issues can take the form of converging too little or too much. Both conditions result in the aforementioned eyestrain and blurred vision. Horizontal prism helps the eyes work together more comfortably when viewing intermediate and near objects.
Conclusion
Computer eye fatigue syndrome is an increasing concern and problem today. OSHA estimates that as many as 90% of the United States work force have this condition to one extent or another. It not only causes discomfort for the individual but a decrease in productivity and enjoyment for the ever increasing computer using population. It is the job of the ECP to not only uncover these issues but to help his or her patients by providing the correct computer lens to ease this situation. Careful questioning of your patient’s visual habits will translate into more sales of these computer specific lenses. But more importantly, by helping patients see clearly at all distances for greater lengths of time, the ECP is improving the quality of their patient’s lives. And isn’t that why we became ECP’s in the first place?
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